In a communications network, use of the communications resources, such as the radio frequency spectrum can be shared between the stations of the network. In such case, the network stations in the network are each allocated zero, one, or more than one channel from a plurality of available communication channels. A channel can be associated with, for instance, one or more of: a time slot; e.g. in the case of FDMA, a frequency range (FDMA); and a transmission code (CDMA). The quality of a channel for one network station may be different from the quality of the channel for another network station. Moreover, for a given network station, the quality of one channel may be different from the quality of another channel. It is therefore possible to improve the quality of communications by appropriately allocating channels for each network station. A network station may be allocated multiple channels, which need not be contiguous.
As the number of channels that may be allocated increases, efficiency gains may be made by optimally allocating from a larger selection of channels. Packet data transmissions, as opposed to circuit-switched data transmission, may benefit from statistical multiplexing as the number of channels increases. For example, second and third generation cellular systems use forms of dynamic channel allocation, with the aim of allocating the desired quantity of resource to each network station. The increasing use of Orthogonal Frequency Division Multiplexing (OFDM) technology, for example in the proposed Long Term Evolution (LTE) cellular system, allows an even larger number of channels to be available.
In a cellular network, channels are usually allocated by a central station, often referred to as a base station. The network stations communicate exclusively with the base station and do not communicate directly with one another. In other types of network, one of the network stations may allocate channels between network stations. Each network station may communicate with one, more than one, or all of the other network stations. In either case, each of the network stations reports channel quality information to the station responsible for channel allocation, and that station then allocates channels and transmits an identification of the respective allocated channel or channels to each of the other network stations.
A known technique, proposed for LTE systems, uses a single bit to represent whether or not each channel is allocated to the respective network station. For example, a transmission of ‘01001’ to a network station may indicate that the second and fifth channels of a set of five available channels have been allocated to that network station. However, the number of data bits needed to indicate the channel allocation thereby increases linearly as the number of channels increases. An increased quantity of allocation data can offset and even eliminate any efficiency gain that might be introduced due to the increased available selection of channels.
One approach to mitigate this problem is to allocate channels in groups. One way of doing this is to require that these groups contain a contiguous set of channels. Then, the group can be described in two fields: one indicating the channel on which the group starts; and the other indicating the number of channels in the group. This technique is used in High Speed Downlink Packet Access (HSDPA) and Digital Audio Broadcasting (DAB) systems, for example.
Another way to achieve this is to group channels together in a fixed way and allocate these fixed groupings amongst the network stations. This is proposed for the Long Term Evolution (LTE) cellular systems. In these approaches, there may some efficiency gains over previous techniques due to the use of a larger selection of channels and by minimising the additional overhead information needed to control those channels, by allocation groups of channels together. Nevertheless, there is the potential for further efficiency gains if the overhead information required to allocate channels can be further reduced.